**4. Laser photoacoustic spectroscopy as a method for breath VOCs detection**

The analysis of trace gases from human breath for medical monitoring and diagnostics and require gas sensors characterized by high sensitivity and selectivity (to avoid interference from other potential interfering species), multi-component capability, real time measurements, large dynamic range, in situ measurements, ease to use. Laser photoacoustic spectroscopy (LPAS) is sufficiently sensitive and

rapid to allow the simultaneous analyses of several trace gas metabolites in single breath exhalations. Over the years, the LPAS technique has demonstrated its ability to detect traces of gas in fields such as biology and medicine due to several factors, such as: real-time detection of one or more volatile compounds, detection limits ranging from ppm (parts-per-million) to ppb (parts-per-billion), high sensitivity and selectivity, use of a single breath collection from a small sampling volume (few 100 ml) without the need for further preparation [66–68, 75–82].
